Glucoamylase enzymes (α-1,4-glucan glucohydrolases, E.C.3.2.1.3.) are starch hydrolyzing exo-acting carbohydrases. Glucoamylases catalyze the removal of successive glucose units from the non-reducing ends of starch or related oligo and polysaccharide molecules and can hydrolyze both linear and branched glucosidic linkages of starch (amylose and amylopectin).
Glucoamylases are produced by numerous strains of bacteria, fungi, yeast and plants. Particularly interesting glucoamylases are fungal enzymes that are extracellularly produced, for example from strains of Aspergillus (Boel et al., (1984) EMBO J. 3:1097-1102; Hayashida et al (1989) Agric. Biol. Chem. 53:923-929; U.S. Pat. No. 5,024,941; U.S. Pat. No. 4,794,175; and WO 88/09795), Talaromyces (U.S. Pat. No. 4,247,637; U.S. Pat. No. 6,255,084 and U.S. Pat. No. 6,620,924), Rhizopus (Ashikari et al. (1986) Agric. Biol. Chem. 50:957-964; Ashikari et al. (1989) App. Microbiol. and Biotech. 32:129-133 and U.S. Pat. No. 4,863,864), Humicola (WO05/052148 and U.S. Pat. No. 4,618,579) and Mucor (Houghton-Larsen et al., (2003) Appl. Microbiol. Biotechnol., 62: 210-217). Many of the genes, which code for these enzymes have been cloned and expressed in yeast and fungal cells.
Commercially glucoamylases are very important enzymes that have been used in a wide variety of applications requiring the hydrolysis of starch. Glucoamylases are used for the hydrolysis of starch to produce high fructose corn sweeteners, and corn sweeteners comprise over 50% of the US sweetener market. In general, starch hydrolyzing processes involve the use of alpha amylases to hydrolyze the starch to dextrins and glucoamylases to hydrolyze the dextrins to glucose. The glucose is then converted to fructose by other enzymes such as glucose isomerases. Glucose produced by glucoamylases can also be crystallized or used in fermentations to produce other end-products, such as citric acid, ascorbic acid, glutamic acid, 1,3 propanediol and others. Glucoamylases are used in alcohol production, such as beer production and sake production. Glucoamylases also find use in the production of ethanol for fuel and for consumption. Recently, glucoamylases have been used in low-temperature processes for the hydrolysis of granular (non-cooked) starch. Glucoamylases are also used in the preparation of animal feeds as feed additives or as liquid feed components for livestock animals.
Although glucoamylases have been used successfully for many years, a need still exists for new useful glucoamylases. The present invention is based upon the finding of novel glucoamylases suitable for use in various applications and particularly starch conversion processes.